In an LTE-A (long-term evolution-advanced) system, coordinated multipoint (CoMP) transmission technologies are introduced to enhance performance of a cell-edge user as well as increase an average throughput of the cell. The following three schemes are standardized in a downlink CoMP technologies of LTE-A R11: joint transmission (JT), dynamic point selection and coordinated scheduling/beamforming. In order that link adaptive transmission is performed accurately and a gain of CoMP transmission is obtained effectively, user equipment (UE) needs to feed back accurate PMI (precoding matrix indicator)/CQI (channel quality indication)/RI (rank indication) information for various transmission assumptions. A feedback scheme where each CSI-RS (channel state indication-RS) resource is at least supported was decided in the 3GPP RAN1 67 conference. And it was decided in the 3GPP RAN1 68 conference that a CoMP measurement set supports at most three CSI-RS resources. As a mobile station is limited with respect to an actual processing ability, a concrete number of reported CSI will be further limited. Actually, there exists a tradeoff between feedback overhead and system performance gain. Relatively more feedback information is advantageous to the system in acquiring a gain of the CoMP transmission; on the other hand, it increases overhead of uplink feedback.
In an LTE Rel. 10 system, periodic and aperiodic feedback manners are used to provide an eNB with feedback information of different granularities, so as to improve performance of the system. Aperiodic feedback has advantages of high capacity of feedback and low time delay, and fits feedback demand of CoMP. Hence, an effective triggering mechanism is needed to be designed to support aperiodic feedback in CoMP transmission.
Currently, aperiodic feedback is triggered via DCI (dynamic control information). When a user is not configured with multicarrier transmission, a 1-bit CSI request domain in DCI format 0 or DCI format 4 is employed to trigger aperiodic report of a corresponding mode; and when the user is configured with multicarrier transmission, a 2-bit CSI request domain in DCI format 0 or DCI format 4 is employed to trigger aperiodic report of a corresponding mode. As shown in Table 1, 00 denotes that report is not triggered, 01 denotes aperiodic report of a primary carrier is triggered, and 10 and 11 denote report of a set 1 and a set 2 configured by a high layer is triggered. Wherein, the set 1 and set 2 are configured via high-layer signaling, the high-layer signaling indicating via 8-bit bitmap information which of 8 subcarriers need to be reported. At present, as at most 5 subcarriers are supported in an LTE-A system, at most 5 bits are actually configured as 1; that is, subcarriers to which bits configured as 1 correspond need to be reported. Furthermore, when aperiodic report is triggered in a common search space, in order to meet length demand of DCI, triggering of 1-bit signaling is only supported. When the user is configured with multicarrier transmission, in consideration that carrier reconfiguration is an important scenario for transmitting DCI in a common search space, when 1-bit triggering signaling is configured as 1, only CSI of a downlink carrier (which is defined in a system information block 2) corresponding to triggering an uplink aperiodic feedback carrier is fed back.
TABLE 1Interpretation of meanings of CSI domainsValues of CSIrequest domainsExplanations‘00’Aperiodic CSI report is not triggered‘01’Aperiodic CSI report of a serving cell c istriggered‘10’Aperiodic CSI report of a set 1 of a serving cellconfigured by a high layer is triggered‘11’Aperiodic CSI report of a set 2 of the serving cellconfigured by a high layer is triggered
It was found by the inventors in the implementation of the present invention that CSI fed back by a user includes rank indication (RI), precoding matrix indicator (PMI) and channel quality indication (CQI) information. An eNB configures each piece of CSI with CSI-RS resource of non-zero power and a measurement resource of interference part, and the user uses these resources to measure and report the CSI. In CoMP transmission, as multiple pieces of CSI (corresponding to different transmitting points and interference assumptions) need to be reported, feedback overhead is very large.
It should be noted that the above description of the background art is merely provided for clear and complete explanation of the present invention and for easy understanding by those skilled in the art. And it should not be understood that the above technical solution is known to those skilled in the art as it is described in the background art of the present invention.